1. Field of the Invention
This invention relates to a process of drying sulfide ores in direct contact with hot drying gases, wherein the sulfide ores are processed with production of SO.sub.2 -containing gases, sulfuric acid is produced from the SO.sub.2 -containing gases in a contact process plant, and the drying gases are heated up with surplus heat from the contact process plant.
2. Discussion of Prior Art
Sulfide ores or ore concentrates, such as copper, nickel, lead, tin and iron ores, and optional admixtures, such as sand, lime, and metal concentrates recovered from slags, must sometimes be dried before their metallurgical processing. The metallurgical processing may succeed a roasting treatment or the roasting may be effected at the same time as the metallurgical processing. The SO.sub.2 -containing gases thus produced are processed in contact process plants to produce sulfuric acid. Particularly in processes in which the roasting and metallurgical processing are performed at the same time, the material must be dried to a very low water content in order to ensure favorable ignition behavior of the ores. On the other hand, the ignitability of the ores must be taken into account during the drying because an ignition during drying must be prevented. This is ensured in that the inlet temperature of the drying gases is properly selected in consideration of the oxygen content of the gases and of the flow pattern of the gas and solids. Drying is generally effected with hot flue gases, which are produced by a combustion of solid fuels. Because a considerable quantity of heat is needed for the evaporation of the water, primary energy is required in a large quantity.
From "Metall", Vol. 37, No. 4, April 1983, page 299 it is also known to use hot air for a drying of copper ores and to heat up said air with surplus heat from the contact process plant. That practice saves a corresponding quantity of primary energy. But that saved quantity of primary energy must be replaced by high-temperature surplus heat, which becomes available in the contact process plant during the processing of gases having a high SO.sub.2 content and which could otherwise by used to produce high-pressure steam.
It is an object of the invention to minimize the use of high-grade heat for drying.